Abstract
We have established that increase in magnesium concentration in LiNbO3:Mg(0.19-5.91 mol% MgO) crystals leads to re-structuring in defective structure and optical anomalies connected with the re-structuring. The anomalies have threshold character. Optical uniformity of crystals was shown to increase at Mg concentration close to a threshold one ~3.0 mol% MgO. IR-absorption spectrum in the area of stretching vibrations of OH groups shifts to a high-frequency area (~50 cm-1 in comparison with other crystals), when Mg concentration nears the second threshold. At this sharp decrease in protons amount and jump-like shift of an absorption edge in the shortwave region are also observed. The shift was shown to be caused by the fact that at 5.5 mol% MgO all point defects NbLi are substitutes by Mg cations and with an increase in Mg concentration, Mg cations occupy Li and Nb sites forming point defects MgLi and MgNb.
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